Representational State Transfer (REST) is an architectural style for distributed hypermedia systems that Roy Thomas Fielding described in his dissertation Architectural Styles and the Design of Network-based Software Architectures in 2000. An architecture style is the combination of various features of an IT system. A style contains rules or patterns to structure a system of different elements and connections. In contrast to design patterns, architectural styles describe the structure of a system as a whole and not the individual subcomponents and classes.

Grundlagen Representational State Transfer

Layered System

The system must be built up in several layers. One layer offers the one lying above it

Shift certain services. In addition, the implementation details of a layer should be encapsulated from the outside world by an interface. Using

of layers, can reduce the dependencies between different components.

However, this concept has the disadvantage that all queries go through the different layers

must be passed through.

Code On Demand

Code on Demand is an optional requirement that states that the server has functionality

manipulate a client by transferring scripts.

Constraints des REST-Architekturstils

The REST architectural style describes six constraints that an application observes

must be in order to be labeled as RESTful.

Client-Server
In general, the same properties apply to a REST architecture as to a client / -

Server architecture. The server is a web application and the client is a browser

or another application. By separating the user interface from the server component, clients are platform-independent.

Stateless
The communication must be stateless, i.e. a message contains all information that is necessary for the client or the server to interpret it

can. Scalability is improved because no states have to be saved between requests

Cache
Clients and servers are allowed to cache messages. To do this, the messages must contain information as to whether caching is permitted. This is necessary for the

Client does not use any out-of-date information. Caching allows some of the

Client-server interactions are avoided, thereby improving performance.

Uniform Interface  

• The central requirement that distinguishes the REST architecture style from other network-based architecture styles is the definition of a uniform interface between clients and servers. The interface must in turn meet four properties: The server does not make its capabilities available as a set of services and operations, but as resources that are identified via a URI. All information or objects such as B. Images, documents or people are mapped as a resource.
• The representation of a resource is not fixed. This means that a server can deliver a resource in various representations such as JSON or XML. A client that has a representation of a resource available has all the information to delete or edit this resource from the server.
• The representation of a resource is not fixed. This means that a server can deliver a resource in different representations such as JSON or XML. A client to which a representation of a resource is available has all the information to delete or edit this resource from the server.
• The communication of a client with the server takes place via the standard methods GET, PUT, POST, DELETE and PATCH and not via application-specific operations.
• The flow of control is controlled via hypermedia, also called HATEOAS. This means that the server tells the client which interactions are possible next when there are queries. A REST client then only needs a single entry URL and can dynamically request all the necessary information from the resources. The server can provide this information via hypermedia controls such as links. As a result, changes in the REST interface do not necessarily have to be adapted in the implementation of the client.

Richardson Maturity Model

To determine how strictly a service is based on REST, Leonard developed Richardson

with the REST Maturity model a four-level scale. In the following table are

the individual stages shown. All low level requirements must be from

einem höheren Level erfüllt sein.

0 • Only uses HTTP as a transport protocol for its own functions

(Tunnel).
• Only uses a single HTTP method (e.g. POST).

• The content can be presented in any format.

• There is only one end point available. 1 • Several resources and thus different end points are available

Disposal. 2 • Uses multiple HTTP methods.

• HTTP protocol is no longer a tunnel.

• Uses HTTP status codes. 3 • Uses HATEOAS